With all the recent posts on the subject, I
guess it's time to republish the follow-up article to the original article
that some are still referring to. . .
_________________________________________________
Jose R. Camara [camara@quantacorp.com] wrote in article 350488E2.C3E63ED8@quantacorp.com...
Almost two months ago I posted some results
of tests done with the Cherokee FR-465.
Since then I found that the meter I had been
using was not working well, as its termination was bad. The power measurements
were somewhat accurate, but were not based on a 50 ohm resistive load.
I repeated the measurements using another
meter:
U= battery
voltage
Pmx= maximum RF power
on a 50 ohm load (APC pot to max)
Imx= battery current
consumption at Pmx output
P= maximum
RF power on a 50 ohm load (original APC setting)
I= battery
current consumption at P output
ERP= Pmx minus 2dB for
guestimated antenna loss
Umin Pmx
Imx P I
ERP
(V) (W)
(A) (W) (A)
(W)
4.0 0.2
0.26 0.2 0.26
0.13
4.5 0.3
0.31 0.3 0.31
0.19
5.0 0.45
0.36 0.45 0.36 0.28
5.5 0.6
0.40 0.6 0.40
0.38
6.0 0.8
0.44 0.8 0.42
0.5
6.5 1.0
0.48 0.8 0.40
0.63
7.0 1.18
0.52 0.8 0.40
0.74
7.5 1.4
0.56 0.8 0.40
0.88
8.0 1.62
0.60 0.8 0.40
1.02
From this new table, one can see that the
output power, on an original radio, doesn't depend on battery power as
long as it is above about 6V. On a modified radio, it will always be higher
with higher voltage.
Measured 'original' 0.8W isn't above FCC limits,
as the FCC limit is 0.5W ERP, which is power radiated by a 0.5W output
stage to a half-wave dipole antenna (about 13" long). If we assume a 2dB
loss for the tiny rubber-duck, we would get 0.5W ERP.
I also measured the battery meter response
with better accuracy:
| (blinking) < 5.13V
|
5.14 - 5.61V
||
5.62 - 6.06V
|||
6.07 - 6.29V
||||
6.30 - max
For added convenience, I measured the
power at the battery meter thresholds:
Battery V Output power
'Original' radio
(V)
(W)
| (blinking) < 5.13
< 0.60
< 0.60
|
5.14 - 5.61
0.60 - 0.75
0.60 - 0.75
||
5.62 - 6.06
0.75 - 0.82
0.75 - 0.80
|||
6.07 - 6.29
0.82 - 0.95
0.80
||||
6.30 - max
0.95 - max
0.80
WARNING!!! Cherokee is now adding diodes
from the DC jack to the battery terminals. That means that if you have
alkaline batteries inside and connect a DC with a voltage 04-0.6V higher,
it will attempt to charge them. The advantage of doing this is that you
can use standard nicad cells and charge them using the dc jack, but I think
they should add a warning in the manual. I chose to remove the diode...
Jose R. Camara